It's a combination of being intellectually lazy+familial influence+narcissism+lack of perspective. Not really that complicated once you realize that all of this

It's a combination of being intellectually lazy+familial influence+narcissism+lack of perspective. Not really that complicated once you realize that all of this is reinforced and forms a feedback loop throughout these individuals' lives because they tend to congregate and be friends (thus, more likely to show their true feathers) with others who are just like them.